Posted
by
kdawson
on Thursday July 19, 2007 @10:18AM
from the 6,000-skulls dept.

Invisible Pink Unicorn writes "Researchers at the University of Cambridge have combined studies of global human genetic variations with skull measurements worldwide to show conclusively the validity of the single origin hypothesis. The alternative hypothesis contended that different populations independently evolved from Homo erectus to Home sapiens in different areas. The lead researcher explains, 'The origin of anatomically modern humans has been the focus of much heated debate. Our genetic research shows the further modern humans have migrated from Africa, the more genetic diversity has been lost within a population. However, some have used skull data to argue that modern humans originated in multiple spots around the world. We have combined our genetic data with new measurements of a large sample of skulls to show definitively that modern humans originated from a single area in Sub-saharan Africa.' The article abstract is available from Nature."

Perhaps one day, when life started out, there were many different types of bacterial lifeforms. Turns out that only a handful managed to stay alive in the ever-changing environment. Some of those just happened to have the bad luck of being wiped out by a meteor shower. And one of few remaining ones was a bloodthirsty killer that ate the few remaining other species; we decended from that guy.

Perhaps something completely different happenned. The chances of a lifeform being succesful in it's environment is likely something so small, the number of digits would overflow this comment box. Just count yourself lucky you were born from the odd chance that one lifeform did manage to survive.

Don't forget that you're only seeing the survivors. It's possible that several variations of primeval life did arise, but one variation out-competed the others, or was the sole survivor of some catastrophe. The fossil record, fragmentary as it is, has numerous examples of whole species groups going extinct, and there's no reason to imagine that life was any less challenging or competitive before it could form fossils.

I am not a scientist, nor do I play one on TV. But my understanding of the way evolution worked is that you need a breeding population sharing common mutations and traits in order to lock in evolutionary traits. The old textbook example for regular speciation within a main population a fertile jungle valley split in two by a great river. Species A was once on both sides of the river and populations could interbreed if presented the opportunity. But given enough isolation, and especially if any environmental factors differ on one side or the other, a Species B can emerge. When the changes are minor, one could refer to the changed one as a sub-species. If the changes become very pronounced, such that interbreeding is difficult or rarely results in viable offspring, then you could say that second population constitutes a new species.

Given that two identical populations can drift away from the ability to interbreed through nothing more than isolation, how likely would it be that one species, scattered across many environments, could independently evolve into a new species whose members could interbreed? That seems a bit off!

I do think that hybrid species are pretty cool, even though they don't occur too often in nature. We had the polar/kodiak hybrid shot a year or so back. Zoos also have many examples of lygers, tylons, etc. Wolves and domestic dogs can interbreed, the same goes with cyotes and jackals as well. It does make one wonder how far humans could drift apart if several populations were isolated for 20,000 years. I wonder if they'd all still look alike except for different bumpy foreheads?

Can more variation in Africa really prove anything beyond... more variation in Africa?

I have a degree in anthropology. I recall some mathematical work in populations and genetics that shows that the place with the most diversity is the origin of the species. That because the species has been in that location so long, they've had more time to mutate and spread those genes a lot. I didn't really understand it, but it was highly mathematical.

Anyways, some anthropologist took this population/genetics research and applied it to human populations. First off, they had to show that there was more diversity in Africa. They did this with genetics. So then if Africa has the most human diversity, and the above postulate about populations and diversity is true, then humans must have originated in Africa.

It might be relevant to the question of whether H. sapiens sapiens had a single origin, which would be a different question. (A subspecies without a single origin would seem to be less surprising; a species with multiple origins would be, AFAIK, rather unusual.)

I don't think it's that unusual. There are plenty of species complexes out there. Probably the most familiar example is genus Canis (dogs). A large number of the members of this family are reproductively compatible, and gene flow between various populations ranging from domesticated dogs, wolves and coyotes (and other wild dogs) still occurs where territories overlap. It's also reasonably common in plant populations.

If Neandertal's and moderns were capable of producing viable, reproductively-capable offspring, then one would expect to find in the molecular data some reflection of a more ancient origin. The mtDNA research thus far indicates not, but there's still some possibility as we peer into Neandertal nuclear DNA that we may find some links there. That would certainly alter the Out of Africa theory from an exclusionary one to having to allow for local hominid populations descended from earlier H. erectus migrations having to be counted into the mix.

Let's be clear, though, that even making allowances for Neandertals contributing to modern human genes still is not the strong statement that the Multiregional Hypothesis makes; namely that a number of modern human populations evolved from earlier hominid migrations out of Africa, and that gene flow has largely kept us homogenous and not lead to reproductive isolation. The growing body of genetic evidence seems to topple the multiregional theory, but doesn't necessarily state that some older populations couldn't have added something to our modern genetic makeup.

Actually, it is simpler than that. Movement out of Africa would occur as small groups leave, to go to other places. Those groups will only carry a subset of the alleles from the larger population. Thus, they will be less genetically diverse.

And it is nice to see another anthropologist on Slashdot. I have my degree in anthropology (focusing in archaeology), with a minor in statistics.;)

Also, people in colder climates would require clothing to stay warm which means they have less skin to expose to the sun, this in turn would increase the need for lighter skin to create more vitamin D.

I should further clarify perhaps, that GOOD science runs from hypothesis to data gathering, testing, and conclusion, while POOR science starts with the conclusion, then gathers evidence, rarely tests (or does not test rigorously enough, or only tests certain applications in which the original conclusion would prove to be true while avoiding or dismissing other testing which might find flaw with it).

"good" science? It's a perfectly valid methodology to devise a theory that isn't supported by evidence and then look for the evidence. I really see no problem with it, and why we should think of it as "bad" science. "bad" science would be science that isn't testable, falsifiable, ignores data, reaches conclusions that don't logically follow, etc. I have no idea if the guy in question produces good science or bad science (as defined above), but then I'm not really addressing that at all.